Hydraulic torque converters, devices used to change the ratio of torque to speed between the input and output shafts of the converter, revolutionized the automotive and marine propulsion industries by providing hydraulic means to transfer energy from an engine to a drive mechanism, e.g., drive shaft or automatic transmission, while smoothing out engine power pulses. A torque converter, arranged between the engine and the transmission, typically includes three primary components: an impeller, sometimes referred to as a pump, directly connected to the converter's cover and thereby the engine's crankshaft; a turbine, similar in structure to the impeller, however the turbine is connected to the input shaft of the transmission; and, a stator, located between the impeller and turbine, which redirects the flow of hydraulic fluid exiting from the turbine thereby providing additional rotational force to the pump.
FIG. 1 illustrates a general block diagram showing the relationship of the engine 7, torque converter 10, transmission 8, and differential/axle assembly 9 in a typical vehicle. FIG. 2 shows a cross-sectional view of a prior art torque converter, shown secured to an engine of a motor vehicle, while FIG. 3 shows a left view of the torque converter shown in FIG. 2, taken generally along line 3-3 in FIG. 2. FIG. 4 shows a cross-sectional view of the torque converter shown in FIGS. 2 and 3, taken generally along line 4-4 in FIG. 3. FIG. 5 shows a first exploded view of the torque converter shown in FIG. 2, as shown from the perspective of one viewing the exploded torque converter from the left, while FIG. 6 shows a second exploded view of the torque converter shown in FIG. 2, as shown from the perspective of one viewing the exploded torque converter from the right. The following discussion is best understood in view of FIGS. 1 through 6.
As described above, the three main components of torque converter 10 are pump 37, turbine 38, and stator 39. The torque converter becomes a sealed chamber when the pump is welded to cover 11. The cover is connected to flexplate 41 which is, in turn, bolted to crankshaft 42 of engine 7. The cover can be connected to the flexplate using lugs or studs welded to the cover. The welded connection between the pump and cover transmits engine torque to the pump. Therefore, the pump always rotates at engine speed. The function of the pump is to use this rotational motion to propel the fluid radially outward and axially towards the turbine. Therefore, the pump is a centrifugal pump propelling fluid from a small radial inlet to a large radial outlet, increasing the energy in the fluid. Pressure to engage transmission clutches and the torque converter clutch is supplied by an additional pump in the transmission that is driven by the pump hub.
In torque converter 10, a fluid circuit is created by the pump, the turbine, and the stator (sometimes called a reactor). The fluid circuit allows the engine to continue rotating when the vehicle is stopped, and accelerate the vehicle when desired by a driver. The torque converter supplements engine torque through torque ratio, similar to a gear reduction. Torque ratio is the ratio of output torque to input torque. Torque ratio is highest at low or no turbine rotational speed (also called stall). Stall torque ratios are typically within a range of 1.8-2.2. This means that the output torque of the torque converter is 1.8-2.2 times greater than the input torque. Output speed, however, is much lower than input speed, because the turbine is connected to the output and it is not rotating, but the input is rotating at engine speed.
Turbine 38 uses the fluid energy it receives from pump 37 to propel the vehicle. Turbine shell 22 is connected to turbine hub 19. Turbine hub 19 uses a spline connection to transmit turbine torque to transmission input shaft 43. The input shaft is connected to the wheels of the vehicle through gears and shafts in transmission 8 and axle differential 9. The force of the fluid impacting the turbine blades is output from the turbine as torque. Axial thrust bearings 31 support the components from axial forces imparted by the fluid. When output torque is sufficient to overcome the inertia of the vehicle at rest, the vehicle begins to move.
After the fluid energy is converted to torque by the turbine, there is still some energy left in the fluid. The fluid exiting from small radial outlet 44 would ordinarily enter the pump in such a manner as to oppose the rotation of the pump. Stator 39 is used to redirect the fluid to help accelerate the pump, thereby increasing torque ratio. Stator 39 is connected to stator shaft 45 through one-way clutch 46. The stator shaft is connected to transmission housing 47 and does not rotate. One-way clutch 46 prevents stator 39 from rotating at low speed ratios (where the pump is spinning faster than the turbine). Fluid entering stator 39 from turbine outlet 44 is turned by stator blades 48 to enter pump 37 in the direction of rotation.
The blade inlet and exit angles, the pump and turbine shell shapes, and the overall diameter of the torque converter influence its performance. Design parameters include the torque ratio, efficiency, and ability of the torque converter to absorb engine torque without allowing the engine to “run away.” This occurs if the torque converter is too small and the pump can't slow the engine.
At low speed ratios, the torque converter works well to allow the engine to rotate while the vehicle is stationary, and to supplement engine torque for increased performance. At speed ratios less than 1, the torque converter is less than 100% efficient. The torque ratio of the torque converter gradually reduces from a high of about 1.8 to 2.2, to a torque ratio of about 1 as the turbine rotational speed approaches the pump rotational speed. The speed ratio when the torque ratio reaches 1 is called the coupling point. At this point, the fluid entering the stator no longer needs redirected, and the one way clutch in the stator allows it to rotate in the same direction as the pump and turbine. Because the stator is not redirecting the fluid, torque output from the torque converter is the same as torque input. The entire fluid circuit will rotate as a unit.
Peak torque converter efficiency is limited to 92-93% based on losses in the fluid. Therefore torque converter clutch 49 is employed to mechanically connect the torque converter input to the output, improving efficiency to 100%. Clutch piston plate 17 is hydraulically applied when commanded by the transmission controller. Piston plate 17 is sealed to turbine hub 19 at its inner diameter by o-ring 18 and to cover 11 at its outer diameter by friction material ring 51. These seals create a pressure chamber and force piston plate 17 into engagement with cover 11. This mechanical connection bypasses the torque converter fluid circuit.
The mechanical connection of torque converter clutch 49 transmits many more engine torsional fluctuations to the drivetrain. As the drivetrain is basically a spring-mass system, torsional fluctuations from the engine can excite natural frequencies of the system. A damper is employed to shift the drivetrain natural frequencies out of the driving range. The damper includes springs 15 in series with engine 7 and transmission 8 to lower the effective spring rate of the system, thereby lowering the natural frequency.
Torque converter clutch 49 generally comprises four components: piston plate 17, cover plates 12 and 16, springs 15, and flange 13. Cover plates 12 and 16 transmit torque from piston plate 17 to compression springs 15. Cover plate wings 52 are formed around springs 15 for axial retention. Torque from piston plate 17 is transmitted to cover plates 12 and 16 through a riveted connection. Cover plates 12 and 16 impart torque to compression springs 15 by contact with an edge of a spring window. Both cover plates work in combination to support the spring on both sides of the spring center axis. Spring force is transmitted to flange 13 by contact with a flange spring window edge. Sometimes the flange also has a rotational tab or slot which engages a portion of the cover plate to prevent over-compression of the springs during high torque events. Torque from flange 13 is transmitted to turbine hub 19 and into transmission input shaft 43.
Energy absorption can be accomplished through friction, sometimes called hysteresis, if desired. Hysteresis includes friction from windup and unwinding of the damper plates, so it is twice the actual friction torque. The hysteresis package generally consists of diaphragm (or Belleville) spring 14 which is placed between flange 13 and one of cover plates 16 to urge flange 13 into contact with the other cover plate 12. By controlling the amount of force exerted by diaphragm spring 14, the amount of friction torque can also be controlled. Typical hysteresis values are in the range of 10-30 Nm.
It should be noted that spatial terminology, as used in the specification and the claims herein, is defined as follows. FIG. 7A is a perspective view of cylindrical coordinate system 80 demonstrating spatial terminology used in the present application. The present invention is at least partially described within the context of a cylindrical coordinate system. System 80 has a longitudinal axis 81, used as the reference for the directional and spatial terms that follow. The adjectives “axial,” “radial,” and “circumferential” are with respect to an orientation parallel to axis 81, radius 82 (which is orthogonal to axis 81), and circumference 83, respectively. The adjectives “axial,” “radial” and “circumferential” also are regarding orientation parallel to respective planes. To clarify the disposition of the various planes, objects 84, 85, and 86 are used. Surface 87 of object 84 forms an axial plane. That is, axis 81 forms a line along the surface. Surface 88 of object 85 forms a radial plane. That is, radius 82 forms a line along the surface. Surface 89 of object 86 forms a circumferential plane. That is, circumference 83 forms a line along the surface. As a further example, axial movement or disposition is parallel to axis 81, radial movement or disposition is parallel to radius 82, and circumferential movement or disposition is parallel to circumference 83. Rotation is with respect to axis 81.
The adverbs “axially,” “radially,” and “circumferentially” are with respect to an orientation parallel to axis 81, radius 82, or circumference 83, respectively. The adverbs “axially,” “radially,” and “circumferentially” also are regarding orientation parallel to respective planes.
FIG. 7B is a perspective view of object 90 in cylindrical coordinate system 80 of FIG. 7A demonstrating spatial terminology used in the present application. Cylindrical object 90 is representative of a cylindrical object in a cylindrical coordinate system and is not intended to limit the present invention is any manner. Object 90 includes axial surface 91, radial surface 92, and circumferential surface 93. Surface 91 is part of an axial plane, surface 92 is part of a radial plane, and surface 93 is part of a circumferential plane.
Some torque converters include a vibration damper assembly which is constructed separate from the remaining torque converter assembly. For example, FIG. 8 shows a perspective view of prior art vibration damper 100, while FIG. 9 shows a front plan view of vibration damper 100 showing a portion of a turbine hub inserted therein. FIG. 10 shows a cross-sectional view of vibration damper 100 taken generally along Line 10-10 of FIG. 9 showing a turbine hub inserted therein. The following is best understood in view of FIGS. 8 through 10. Vibration damper 100 includes a plurality of damper springs 102 each arranged within an opening 103. As can be seen in the figures, damper springs 102 may be constructed of more than one spring, e.g., outer spring 104 and inner spring 106, thereby providing for different types of damping effects than a single spring configuration. Vibration damper 100 further includes cover plates 108 and 110 and flange plate 112 disposed therebetween. Damper hub 114 comprises outer spline 116 having a plurality of teeth 118 and spaces 120 and inner spline 121. Cover plate 108 includes outer spline 122 having teeth 124 and spaces 126, and inner spline 128 having long teeth 130, short teeth 132 and spaces 134. Hub spline 116 is arranged to rotationally connect to cover plate inner spline 128 so that long teeth 130 are disposed within spaces 120 and short teeth 132 are disposed about outer circumferential surface 133 of teeth 118; however, as can be seen in the figures, spaces 120 are larger than teeth 130 thereby providing for rotational movement of flange plate 112 against damper springs 102, i.e., to provide vibration damping.
It should be appreciated that by rotationally connected, or secured, we mean that hub spline 116 and cover plate inner spline 128 are connected such that the two components rotate together, that is, the two components are fixed or partially fixed, i.e., lash is present, with respect to rotation. Rotationally connecting two components does not necessarily limit relative movement in other directions. For example, it is possible for two components that are rotationally connected to have axial movement with respect to each other via a spline connection. However, it should be understood that rotational connection does not imply that movement in other directions is necessarily present. For example, two components that are rotationally connected can be axially fixed one to the other. The preceding explanation of rotational connection is applicable to the discussions infra. In the discussions infra, a connection is assumed to be a rotational connection unless otherwise specified.
Unlike the above described vibration damper arrangement which is within the torque transmitting path only during clutch lock-up, vibration damper 100 may receive and transmit torque during both clutch lock-up and turbine mode. During clutch lock-up, cover plate 108 is driven by a clutch plate (not shown) via outer spline 122. In this instance, torque is transmitted from a clutch plate to cover plate 108 via outer spline 122, from cover plate 108 to springs 102 via contact between walls 136 and springs 102, from springs 102 to flange plate 112 via contact between springs 102 and walls 138, from flange plate 112 to damper hub 114 via the connection between flange plate 112 and damper hub 114, e.g., weld 140, from damper hub 114 to an input shaft of a transmission (not shown). Contrarily, in turbine mode, torque passes from the turbine, as described above, to turbine hub 142, from turbine hub 142 through teeth 144 of spline 146 to cover plate 108 via long and short teeth 130 and 132, respectively, from cover plate 108 to springs 102 via contact between walls 136 and springs 102, from springs 102 to flange plate 112 via contact between springs 102 and walls 138, from flange plate 112 to damper hub 114 via the connection between flange plate 112 and damper hub 114, e.g., weld 140, from damper hub 114 to an input shaft of a transmission (not shown).
It should be appreciated from the figures that only cross sections of teeth 144 are shown in FIG. 9, while a cross section of the entire turbine hub 142, including teeth 144, is shown in FIG. 10. As can be seen in the figures, spaces 134 may be slightly larger than teeth 144. Thus, during manufacture of a torque converter, turbine hub 142 may be more easily inserted within vibration damper 100. Unfortunately, due to this difference in size, an undesirable rattle is created within the assembly, as turbine rotation speeds up or slows down and clutch lock-up and release occurs. This rattle is due to lash between turbine hub spline 146 and cover plate inner spline 128, i.e., the movement of teeth 144 within spaces 134. Although spaces 134 could merely be decreased in size and thereby reduce lash, assembling a torque converter would become increasingly difficult as it would be more difficult to insert teeth 144 within spaces 134. As one of ordinary skill in the art should understand, increasing assembly difficulty also increases the cost of assembly and thereby the overall cost of a torque converter.
As lash and/or rattle are undesirable, methods and means of reducing such lash are desirable and necessary improvements to vibration dampers. And, as can be derived from the variety of devices and methods directed at reducing such lash, many means have been contemplated to accomplish the desired end, i.e., quiet, smooth, rattle/lash-free operation of a vibration damper. Heretofore, tradeoffs between lash and cost of assembly were required. Thus, there is a long-felt need for a lash-free vibration damper which is easy to assemble.